A search for new physics in events with one lepton, high jet multiplicity and high b-tagged jet multiplicity

Abstract

We present a search for new physics in events with one lepton and at least six jets. We characterize the signal as an excess of events with a large number of jets tagged as originating from b quarks. The search is performed on 19.3 ${\rm fb}^{-1}$ of $\sqrt{s} = 8$ TeV LHC proton-proton data. The result is interpreted in the context of supersymmetric models with R-parity violation and minimal flavor violation, in particular with pair-produced gluinos decaying each to a top, a bottom, and a strange quark.

Link to PAS

Note to CMS speakers

The $N_b$ plots in the next section are meant to be displayed on a computer screen and can be confusing if projected. If you intend to include these plots in your slides please use their versions attached below with names "nBjetMu(Ele)_nj_pro.pdf".

Plots and Tables from SUS-12-015 PAS

Table 1. Summary of expected background, expected signal for $m_{\tilde g}$ = 1 TeV, observed yields and total background after the (background only) fit for the muon samples considered in the analysis. We report the total uncertainty on the predicted yield.

Table 2. Summary of expected background, expected signal for $m_{\tilde g}$ = 1 TeV, observed yields and total background after the (background only) fit for the electron samples considered in the analysis. We report the total uncertainty on the predicted yield.

Figure 1. Distribution of the number of b-jets for events with one muon (top) or electron (bottom) and 6 jets, compared to the background prediction from simulation corrected for the b-tagging response in data. The red band represents the uncertainty originating from the error on the b-tag correction factors.

Figure 2. Distribution of the number of b-jets for events with one muon (top) or electron (bottom) and 7 jets, compared to the background prediction from simulation corrected for the b-tagging response in data. The red band represents the uncertainty originating from the error on the b-tag correction factors.

Figure 3. Distribution of the number of b-jets for events with one muon (top) or electron (bottom) and at least 8 jets, compared to the background prediction from simulation corrected for the b-tagging response in data. The red band represents the uncertainty originating from the error on the b-tag correction factors.

Figure 4. Distribution of the number of b-jets for events with one electron, one muon, and $N_{\rm jets}$ = 4 (top) or $N_{\rm jets}$ = 5 (bottom) in data, compared to the background prediction from simulation corrected for the b-tagging response. The cerulean band represents the total uncertainty on the background yield.

Additional Material

Figure 7. Signal efficiency as a function of the gluino mass for the $\tilde g \to$ tbs RPV simplified model. top(bottom): after the muon(electron) baseline selection for events with exactly 6 jets (purple), 7 jets (red) and $\geq$8 jets (orange). The error includes both statistics and systematics, excluding the PDF uncertainty. The efficiency is computed putting at the denominator the total signal yield and not the total yield times the semileptonic branching ratio

Reinterpretations

When reinterpreting this analysis with another signal model, you will need signal efficiencies and the appropriate background yield and error.
The total signal efficiency is shown in Figure 7 for $N_b \geq 1$. As discussed in the Figure caption, it is computed putting at the denominator the total signal yield and not the total yield times the semileptonic branching ratio. The efficiency with its total error (including the PDF systematic) is also attached in table form below. For convenience efficiencies in the table are multiplied by a factor of $10^2$.
The total efficiency should be used to rescale the fractional efficiency in each b-jet bin that is roughly independent of the gluino mass and can be deduced from the event yields reported in Tables 1 and 2 above.
While interpreting the result it should be noted that the relevant error on the background is that on the shape, which corresponds to the post-fit error in Tables 1 and 2, rather than the pre-fit error in the first line of the tables, which includes also the normalization error. However, if you wish to use the analysis results to construct counting experiments, the appropriate error on the background is the one on the yield, listed in the first line of the tables.
The limit in Figure 6 is also attached to this twiki in the form of a root tree. The variables contained in the tree are mg=gluino mass (in GeV), obs=observed limit on the gluino cross section times branching ratio (in pb), exp=expected limit (in pb), exp_up=upper bound of the one sigma band for the expected limit (in pb), exp_down=lower bound of the one sigma band (in pb).